Fallout 4: How No Game Ending Mission Makes All The Difference

Clipping Error discuss why the fact that Fallout 4 has no official end is going to make all the difference to players new and old to the series. They talk about how previous games had endpoint missions after which nothing more could be done, since the game ended, but Fallout 4 will be different, and that's going to change things for players when it comes to how they approach missions.

Does this mean that the story will have no closure and no real tension?

It just seems like Bethesda's recent games just want to be endless for the sake of it. What type of quests will we have when there is no "real ending mission"? Will it just be unlimited fetch quests like Skyrim?

No, the game will have a main storyline that will come to an end after that final 'main' mission but you will be able to continue playing the game afterwards (unlike Fallout 3 which ended the game and your play through after that final mission).

I imagine that you will still be able to fortify your base which will still probably continue to be attacked from time to time, and still explore the wasteland. You will be able to finish any side missions that you didn't get around to finishing and continue leveling up non-stop.